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Homework Help: Knowing the Energy of a photon, what is the charge of a species?

  1. Nov 4, 2017 #1
    1. The problem statement, all variables and given/known data
    An atom or ion with only one electron is excited from the ground state to the first excited state (n = 2) with a photon of 1.47E-17 J of energy. What is the charge on the one-electron species?
    A. 0
    B. +1
    C. +2
    D. +3
    E. +4

    2. Relevant equations
    E=-(2.18E-18)(Z2)/(N2)

    3. The attempt at a solution
    I plugged in the information given into the equation:

    (1.47E-17)=(-2.18E-18)(Z2)((1/4)-1)

    With some algebra, I got Z=2.998, which may as well be a charge of +3.
    However, according to the answer key, the correct answer is, in fact, +2 (C).
    I would appreciate any guidance as to where I might be going wrong with this problem. :)
     
  2. jcsd
  3. Nov 4, 2017 #2

    Orodruin

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    What is the charge of the ion as a whole if the charge of the nucleus is 3?
     
  4. Nov 4, 2017 #3
    Due to shielding, the effective charge would be about +2? I think I kinda see that maybe my calculations weren't wrong, but that I didn't understand the question right, but I still don't really get it.
     
  5. Nov 4, 2017 #4

    Borek

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    Staff: Mentor

    You calculated Z, but Z is not what the question asks about. It asks you to calculate charge of the ion, not of the nucleus.
     
  6. Nov 4, 2017 #5
    Ah, so then because I calculated the nucleus' charge to be +3, with a single electron there would be a charge of +2? That would make a lot of sense. Then I assume I didn't make any mistakes in solving for charge of the nucleus to figure out the ion's charge? Thanks!
     
  7. Nov 5, 2017 #6

    Borek

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    Staff: Mentor

    Looks OK, although your first equation and the second equation are different.
     
  8. Nov 5, 2017 #7
    Thanks!
     
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